Weft straightener



Dem-30,1952

Filed- March 22, 1951 'r. M. BERRY WEFT STRAIGHTENER Fig. 1.

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10 )Qv44z y His Avail Patented Dec. 30, 1952 UNITED WEFT STRAIGHTENER Theodore M..Berry, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application March 22, 1951, Serial No. 216,941

This invention relates to weft straightening devices, and more particularly to mechanismsfor automatically straightening bows and skews in the weft threads of moving woven material, i. e., for producing a perpendicular relationship betweenthe weft threads and the warp threads of the material.

There are several devices which have been used heretofore for detecting the presence of and automatically correcting for a bow or a skew in the weft threads of a moving strip of woven material. A major objection to most of these weftstraightening devices is that they are quite complex and expensive. Although some less expensive devices do exist, the less expensive devices have an extremely limited range of operation as far as the type of woven material is concerned. Moreover, forany material they do notoperate on large angles of skew.

Most weft straighteners used heretofore pass several narrow beams of light through a moving strip of woven material so that the light beams are principally modulated by the passage of the weft threads of the material therethrough. The modulated light beams are directed onto photoelectric devices, and the output voltages of the various photoelectric devices and their associated amplifiers are compared with one another to detect a bowor a skew in the material. The voltage comparing systems depend upon a difference in the voltage amplitudes or a difference in the frequencies to detect the bows or skews. However, when large angles of skew or bow are involved, the output voltages of the photoelectric cells and their associated amplifiers are unsuitable for an accurate determination of the bow or skew by amplitude or frequency differences.

Therefore, an important object of my invention is to provide new and improved means for detecting the presence of a bow or a skewin the weft threads of moving woven material.

Another object of my invention is to provide a new and improved device for actuating standard electromechanical weft straightening equipment to correct bows and skews in the 'weft threads of moving woven material.

Thisinvention relies upon a phase difference in the modulation of light beams passed through or reflected from woven material to detect the presence of bows or skews in the weft threads of the material. In carrying out this invention in one embodiment thereof, two rotating beams of lightare focused on a moving strip of woven-material. The light beams'are modu- 3 Claims. (Cl. 26---.51)

lated principally by the weft threadsin the "material as the beams pass through the material. The reflections of the light beams from the material are, of course, also modulated by the warp threads. Either the modulated light beams or the modulatedreflections are directed onto photoelectric devices and cause the photoelectric devices and their associated amplifiers to produce voltages which are similarly modulated. These voltages are passed through demodulators which remove the high frequency components, leaving the modulation voltages. The modulation volt ages are fed to separate phase comparing circuits which produce output voltages proportional to the phase angles between the modulation 'voltages and a standard voltage. These output'voltages are then used to actuate conventional electromechanical bow and skew correcting mechanisms, through acircuit whichapplies a voltage proportional to the sum of the output voltages to the skew correcting mechanism, and a voltage proportional to the difference of the output voltages to the bow correcting mechanism.

For a better andmore complete understanding of my invention, together with additional. objects and advantages thereof, reference should now be had to the following-description, taken in connection with the accompanying drawings, in which:

Fig. 1 is an end view in elevation of a preferred embodiment of my'invention;

Fig. 2 is aview showing the relation of the rotating light beams used in my invention to straight weft threads in a piece of woven material;

Fig. 3 is .a plot of light intensity vs. time for a stationary light beam after it has passed through moving woven material and been modulated by the weft threads thereof, the weft threads and the cross section of the light beam being of substantially the same relative size as shown in Fig. 2;

Fig. 4 i a plot of light intensity vs. time for a rotating light beam after it has passed through movingwoven material and been modulated by the weft threads thereof, the weft thread and light beam being of substantially the same relative size as those shown in Fig.2;

Fig. 5 is a view showing the relation of the rotating light beams "used in my invention to skewed weft threads in apiece of woven material;

Fig. 6 is a view showing the relation of the rotating light beams used in my invention to bowed weft threads in apiece of woven material;

Fig. 7 is a diagram, partially in block and line form, of an electrical circuit for use with an automatic weft straightening device embodying my invention;

Fig. 8 is a plot of one-half of the envelope of the modulated light intensity wave shown in Fig. 4.

Fig. 9 is a schematic diagram of a simplified demodulating circuit suitable for use as a component of the circuit of Fig. 7;

Fig. 10 is a schematic diagram of a simplified phase comparing circuit suitable for use as a component of the circuit of Fig. '7;

Fig. 11 is a simple diagrammatic sketch showing conventional devices for correcting bow and skew in a strip of moving woven material, together with the rotating light sources employed in this invention to actuate such devices; and

Fig. 12 is a view showing the desired relationship of the weft threads to the warp threads in a piece of woven material.

Referring .to the drawing, in Fig. l, spur gear I, which is mounted on the shaft of motor 2, mates with a gear 3 to, drive shaft 4. Mounted on shaft 4 are identical bevel gears and 6, which actuate respectively identical gears and 8. Gear 1 rotates lamp 9 which, with gear I, is rotatably mounted on base I0, while gear 8 in a like manner rotates lamp H on base l2.

Power is supplied to filament 9a of lamp 9, through brushes l3 and I4, and slip rings l5 and I6. Power is similarly supplied to filament Ila. of lamp through brushes l1 and I8, and slip rings 19 and 20.

Lamp 9 produces light beam 2|, of which a cross-section is in effect the image of filament 9a, while lamp produces light beam 22, of which a cross-section is in effect the image of filament Ila. The lengths of the cross-sections of light beams 2| and 22 are thus several times the widths thereof, i.'e. the cross-sections are oblong. Lamps 9 and H are identical lamps and, in this particular embodiment, are mounted so that their respective filaments, 9a and Ila, have the same angular displacement at any instant. In other words, light beams. 2| and 22 here rotate in exact synchronism with each other around their respective longitudinal axes upon rotation of motor 2. i

Light beam 2| is focused on a moving strip of woven material, such as cloth 23, through lens 24, while light beam 22 is focused thereon through lens 25.- Light beam 2| is focused on an area adjacent to one edge of cloth 23, and light beam 22 is focused directly across from light beam 2| onan area adjacent to the other edge of cloth 23. After their passing through cloth 23, light beam 2| falls uponscanner 2B, and light beam 22 falls upon scanner 21. Scanners 26 and 21 are conventional photoelectric devices producing an electrical signal in response to the illumination thereof.

Attached to. motor 2 so as to have its angular position. fixed with respect to light beams 2| and 22 is an alternating-current generator 28. Generator 28 has an output frequency of twice that of the frequency of'rotation of light beams 2| and 22 for a purpose which will appear hereinafter.

Referring toFig. 2,ilight beams 2| and 22 have, as they pass through the moving cloth 23, a width of substantially the same order of magnitude as the diameter of the weft threads 29 of cloth 23. Since as previously stated, the lengths offthe cross-sections of'light beams 2| and 22 areseveral'timesthe widths thereof, when beams '4 2| and 22 are in the position illustrated, no single weft thread can block out either beam entirely at any instant. However, at any time, both beams 2| and 22 will have portions blocked out.

When beams 2| and 22 are rotated degrees around their respective longitudinal axes to positions 2|a and 22a, a single weft thread can block out both beams 2| and 22 entirely at the same time. Conversely, it is also possible at other times, when beams 2| and 22 are in positions 2 la and 22a, for them to pass through cloth 23 without striking weft threads 29 at all. If beams 2| and 22 are held stationary in positions 2|a and 22a, as cloth 23 moves, the intensity of the modulated beams reaching either scanner 26 or 2'! varies as shown in Fig. 3.

If the light beams are continuously rotated in the same direction in synchronism with each other, the intensity of each beam passing through moving cloth 23 is modulated as shown in Fig. 4. The periods of maximum amplitude of oscillation in the light intensity waves occur when beams 2| and 22 are parallel to weft threads 29. The periods of minimum amplitude of oscillation, i. e. relatively steady output, occur when beams 2| and 22 are perpendicular to weft threads 29.

In Fig. 2, as well as in Figs. 5 and 6, the warp threads of strip 23 have been omitted, merely so that the relationship of light beam 2| and 22 to weft threads 29 may be more clearly seen. As shown in Fig. 12 which illustrates the appearance of the warp threads 29a with respect to weft threads 29, when the material has no bow or skew, warp threads 2911 extend parallel with respect to the longitudinal edge of the material, and there is substantial space between the warp threads for the passage of light. Even when weft threads 29 become bowed or skewed, warp threads 29a still extend parallel to the longitudinal edge of the material. Although warp threads 29a at times may block out portions of light beams 2| and 22, it has been found that this does not affect the phase of the light intensity oscillations suificiently to impair the functioning of the device.

If weft threads 29 of moving cloth 2 become skewed as shown in Fig. 5, the peak of the envelope of the modulated light intensity wave of Fig. 4 are advanced by phase angle proportional to the angle of skew. Since beams 2| and 22 are being rotated in synchronism, and the skewed weft threads 29 thus at any instant make the same angle with both beams, the envelopes of the modulated intensities of both beams have substantially the same phase angle.

However, if weft threads 29 are bowed, as shown in Fig. 6, they cross beam 2| at an angle different from that at which they cross beam 22. Therefore, the phase angle of the envelope of the modulated intensity of beam 2| will differ from the phase angle of the envelope of the modulated intensity of beam 22.

Referring to Fig. 7, scanner 26 together with its associated amplifier 30, produces a, voltage having the same Wave shape as the modulated intensity of beam 2|. Similarly, scanner 21 with amplifier 3|, produces a voltage having the same wave shape as the modulated intensity of beam 22. The outputs of amplifiers 3| and 32 are applied respectivelyto demodulators 32 and 33. De-

modulators 32 and 33 each remove the high fre quency components from their respective input voltage and produce an output voltage having the wave shape of half of the envelope of the input. Fig. 8 illustrates a typical wave shape for the output of either demodulator. This wave shape, corresponding to a half-envelope of the modulated voltage, is commonly known as the modulation voltage.

An example of a demodulator suitable for use in this invention is the conventional demodulating circuit illustrated in Fig. 9. This particular circuit includes two rectifying elements 34 and 35, a bleeder resistor 36, a current limiting resistor 31, and a filter capacitor 38, and is energi'zed through a transformer 39 and a coupling capacitor 46. The input voltage to the circuit is thus an A.-C. wave. Rectifier 34 rejects the negative portions of the waves allowing only the positive portions to pass. Bleeder resistor 36 and filter capacitor 38 act to smooth out the rectified signal so that a wave having the shape of the positive envelope is produced at the output terminals of the circuit. By-pass rectifier '35 and resistor 31 pass the negative portions of the input wave to keep the impedance presented to the -am plifier relatively steady throughout the entire oscillations of the input wave.

The modulation voltages produced by demodulators 32 and 33 are fed to conventional phase comparing circuits 4| and 42. The output of generator 28 is also fed into phase comparing circuits 4| and 42. Generator 28, by operating at twice the frequency of rotation of light beams 2| and 22, produces a voltage of the same frequency as the modulation voltages produced by demodul'ators 32 and 33'. Since generator 28 is driven by motor 2, the phase angle of the output of generator 28 is fixed relative to the angular position of the cross-sections of light beams 2| and 22. In the embodiment illustrated, when weft threads 29 are straight as in Fig. 2, the modulation voltages lead the output of generator 28 by a phase angle of 90 degrees. i

In Fig. is shown a conventional phase comparing circuit applicable to this invention. The modulation voltage of the associated demodulator is passed through a conventional clipping circuit comprising two rectifying element 43 and 44, and their biasing voltage sources, and then applied across a resistor 45. Paralleled with resistor 45 is a series circuit including in sequence a rectifying element 46, a load resistor 41, and another rectifying element 48, rectifiers 46 and 48 being connected with opposite polarity so that no current can flow through the series circuit. However, resistors 45 and 41 are both provided with mid-taps and connected therebetween is a resistor 49. Resistor 49 thus completes two separate paths for current flow, one comprising the upper halves of resistors 45 and 41, and rectifying element 45, and the other comprising the lower halves of resistors 45 and 41, and rectifying element 48. The words upper and lower halves refer to the position of the resistors as viewed in Fi 10.

It is across resistor 49 that the output of generator 28 is applied, after it has been passed through a conventional clipping circuit comprising two rectifying elements 56 and 5|, and their biasing voltage sources. The action of the two clipping circuits is such that the standard voltage applied across resistor 49 has an average amplitude of substantially one-half that of the modulation voltage applied to resistor 45.

Now, if the voltages in resistors 45 and 49 are 90 degrees out of phase, as is the condition with straight weft threads, currents of equal magnitude but opposite in direction of flow will flow in the upper and lower halves of resistor 41.

This, of course, results ina total voltage ofzero across resistor 41, and thus in a, zero output volt age, since it is across resistor 41 that theoutput of the circuit is taken. However, if the phase of the modulation voltage shifts, depending upon the bow or skew of the weft threads, the currents in the two halves of resistor 41, although still opposite in direction, will no longer be equal in magnitude. This will result in a D. C. voltage appearing across resistor 41, its polarity depending upon in which direction the phase shift occurred, and its magnitude depending upon the amount of the phase shift.

When the weft threads become skewed, the outputs of both phase comparators 4| and 42 are substantially equal in magnitude and of the same polarity, since the angles between the threads and the light beams are the same for both beams. However, when the weft threads become bowed, the outputs of the phase comparators 4| and 42, although still substantially equal in magnitude, are of opposite polarity, since the angles made by the weft threads with the light beams are on opposite sides of the zero angle, i. e., the angle made when the weft threads are straight.

The output voltages of the phase comparators 4| and 42 are used to actuate conventional bow and skew control mechanisms as shown in Fig. 7. The connection of the center tapped resistor 52 shown therein supplies the sum of the output voltages to amplifier 53, by which the skew control motor 54 is actuated, and a voltage proportional to the difference of the output voltages to an amplifier 55, by which bow control motor 56 is actuated. Thus, when the weft threads are skewed so that voltages equal in magnitude and of the same polarity are produced by the phase comparators 4| and 42, the skew control motor 54 will operate, and the bow control motor 56 will remain at standstill. Motor 54 can rotate in either direction, depending upon the polarity of the voltage impressed upon it; the olarity, of course, varies with the direction of the skew of the weft threads. Conversely, when the weft threads are bowed so that voltages equal in magnitude and opposite in polarity are produced by the phase comparators 4| and 42, the bow control motor 56 will operate and skew control motor 54 will remain dormant. The direction of rotation of motor 56 depends upon the polarity of the voltage impressed upon it and, therefore, upon whether the weft threads are both forward or backward with respect to the direction of movement of the strip of material.

Referring to Fig. 11, in which are shown conventional bow and skew correcting mechanisms, a strip of woven material, such as cloth 23, is passed between a pair of mangle rolls 51 under an idler roller 58, over a canting roll 59, under an idler roll 60, under a bowed roll 6|, over a bowed roll 62, under an idler roller 63, through the rotating light beams 2| and 22 of this invention, and then into a tenter having endless chains 64 and 65. These chains pass around end pulleys 66 and 61, which are driven at equal speeds by suitable driving means, such as the electric motor 68, to which they are mechanically connected.

Canting roll 59, and bowed rolls 6| and 62 respectively comprise conventional skew and bow correcting means. The position of canting roll 59 is varied by skew control motor 54, through suitable mechanical connections. These connections and their manner of elevating and lowering opposite ends of canting roll 58 to correct skew in'ithe weft. threads 'of' cloth 23,. are described in. Patent 2,492,737. granted December 27, 1949, to George B. Dunn and assigned to the same assignee as the present invention.

The positions of bowed rolls and ti are controlled by bow control motor 55. The mechanical connection between rolls 6i and 62 and motor 56, as well as the functioning of the rolls to correct bow in the weft threads, are likewise described in the aforementioned Dunn patent.

The preferred embodiment described herein utilizes light beams rotating in synchronism with each other and a single generator whose output phase angle is displaced 90 degrees under normal straight conditions of the weft threads from the output of the demodulators actuated by the modulated light beams. However, an equally workable device could be constructed in which there is a phase angle between the two rotating light beams and thus a phase angle between the outputs of the demodulating circuits under normal conditions of the weft threads. The phase of the outputs of the demodulating circuits would then be compared directly for how control and 1 the voltage having the phase of the combination of the circuits would be compared with the phase of a standard voltage for skew control.

It should therefore be understood that, while the present invention has been described by reference to a particular embodiment thereof, this is by way of illustration of the principles involved, and that those skilled in the art may make many modifications in the arrangement and mode of operation. Therefore, I plate by the appended claims to cover any such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Leters Patent of the United States is:

1. In a Weft straightener for a strip of material having warp threads and weft threads, means for projecting onto said strip two beams of light directed toward opposite edges of said strip, the cross-section of each of said beams having a length several times as great as the width thereof means for rotating said beams of light around their respective longitudinal axes at identical angular velocities and with a predetermined angular displacement therebetween; two photoelectric devices, each mounted to receive light having a varying intensity dependent upon the modulation of a corresponding one of said beams by said weft threads; a source of periodically varying voltage having a predetermined time phase; and means controlled by said photoelectrio devices in response to the diiference in time phase of the variations in the modulated light received by each of said photoelectric devices with respect to the time phase of said periodically varying voltage for positioning said weft threads perpendicular to said warp threads.

2. In a weft straightener for a strip of woven material having warp threads and weft threads,

conterntwo lampspositioned on one side of theplaneof the strip for projecting onto the strip two beams of light directed toward opposite edges of the strip, the cross-section of each of.said beams having a length several times as greatas the width thereof; a motor for rotating said lamps whereby said beams of light are rotated around their respective longitudinal axes at identical angular velocities and with a predetermined angular displacement therebetween; a pair of photoelectric devices mounted on the opposite side of the plane of the fabric, each in a position to receive light from a corresponding one of said beams transmitted through said strip; a generator driven by said motor for producing a periodically varying voltage having a predetermined time phase; and means controlled by said photo electric cells in response to the difference in the time phase of the variations in said light received by each of said photoelectric devices with respect to the time phase of said periodically varying voltage for positioning said weft threads perpendicular to said warp threads.

3. In a weft straightener for a strip of woven material having warp threads and weft threads, two lamps positioned on one side of the plane of the strip for projecting onto the strip two substantially identical beams of light directed toward opposite edges of the strip at substantially right angles thereto, each of said beams having an oblong cross-section; a motor for rotating said lamps whereby said beams of light are rotated around their respective longitudinal axes at identical angular velocities and with a predetermined angular displacement therebetween; a pair of photoelectric devices mounted on the opposite side of the plane of fabric, each in a position to receive light from a corresponding one of said beams transmitted through said strip; a generator driven by said motor for producing a periodically varying voltage having a predetermined time phase and a frequency double the frequency of rotation of said light beams; and means controlled by said photoelectric cells in response to the difference in the time phase of the variations in said light received by each of said photoelectric devices with respect to the time phase of said periodically varying voltage for positioning said weft threads perpendicular to said warp threads.

THEODORE M. BERRY,

REFERENCES CITED The following references are of record in the Reichelt May 30, 1944 

